Photographic film



Jun 7, 1927.

- w. LO'HOFER PHOTOGRAPIHIC FILM Filed Nov. 5. 1923 TRANSPARENT suPdfi'r w wov EMULSION SENSITIVE To VISIBLE Lmn-r finvs COLLOID LAYERCONTA'NING- F'INELY GRAINED PARTICLES AND IF DESIRED AN ANTIHALATION DYEPatented June 7, 1927.

UNITED STATES wnznnmr Lonorna, or were,

axrmnensnnnscnarr, or

GERMANY, assrenoa '1:0 I. c. rnauxroa'r-ou-rna-mam,

FARBENINDUSTBIE GERMAN-Y.

PHOTOGRAPHIC 'FILM.

Application filed November 8,1928, Serial No. 672,650,..apd in GermanyMarch 9, 1923.

Photographic films are known in which the back is provided with agelatine coating to stop curling. Dyed coatings on the bac of supportsfor photographic purposes are also known in order to avoid halation.

he object of the present invention is a photographic film, the back ofwhich is provided with a coating which not only fulfils the requirementsfor protection against curlm ing and'halation but which aifords at thesame time a suitable ground for retouching. This iseifected-by a layerof a colloid in which substances are embedded that absorb or diffuse anylight transmitted through the coating and thesupport and impart to thecoating a more .or less rough surface. The layer furthermore imparts agreater clearness and softness to the picture, while the softer lightsshow more clearly on the sub clued background and stand out in betterrelief. Softness is desired in photography and is obtained according tovthe invention by the facility afforded by the film coating forretouching. For this purpose one uses ;hitherto a background of a dullvarnish which, however, introduced difliculties in the case of films.

The possibility of retouching depends entirely upon the graininess ofthe layer. The

least size of grain just enabling retouching is within the range ofsizes of the silver rams in a developed photographic image. he grainsize of the layer may be varied according to the desired degree ofretouch,

a as to whether a strong change of the original values of thephotographic image is necessar or whetherthere shall only be applied alitt e correction of a few lines. For example,

a film tor portrait work requires a size of grain difierent from thatsuitable for photo- -mechanical work. Furthermore, the grain size willbe regulated as to whether the film will be used in enlargement or not.In the first case too big a size of grain. would cause trouble. Thegrain size is increased if the possibility of a strong and sharp retouchis desired. \v

The

raininess is determined approximately by t e size and the quantity ofthe single grains present. It has'been found that a layenfittingsatisfactorily for retouch must have at least 15 l to 20 percent ofroughening material in the substratum, the particles having an averagegrain size of l or 2 thousandths of a millito the invention ashereinbefore described.

graphic material,

xin

meter. Opaque coatings now on the market have a grain size of about 3ten-thousandths of a millimeter, Although these coatings have an opticalefiect since they scatter visual rays, they are not at all suitable forretouch.

It is to be understood that theminimum percentage above indicated ofroughening material in the substratum is onlyapproxir mate, since thesize of grains varies not only with the quantity of roughening material,but also insome way with the method of mixing the solution from whichthe coating In the accompanying drawing, which is a 7 diagrammaticalsectional view, 1 represents an ordinary flexible support ofnitrocellulose or the like; 2 is'a gelatine-silver halid emulsionlayerand 3 is a back coating according As the colloid can that can beentirely other elements which be used mainly gelatine or partly replacedby are insoluble in water when the applied solution is dried, forinstance albumen, caseine, and the like treat- 50 ed with formaldehyde.As embedded substances can be used insoluble compositions in a very finestate of division, such as car-' bonates', sulphates and phosphates ofthe' alkaline earths, also suitable compounds of 35 the heavy metals andthe like. The back coating can be applied in the same manner as, forinstance, in roll-films.

To enhance the antihalation efiect dyes or other combinations may beadded, preferablythose which can easily beremoved at the usual latertreatment of the photofor instance in the acid g baths. Suitable dyesfor this purpose are, for example, acid fuchsine, aurin or tartrazine.

. It is to be understood that the. data given below is merely by way ofexample and that the invention is not limited to the use of thearticular substances or proportions speci ed therein.

- Example 1.-A preparation of 1 kilo of rice starch in 5 litres of wateris poured into 30 litresof a solution of 10per cent gelatine and is aplied in the usual manne'rf 10a Ewmnp 2.The material for the back coatingisv prepared by stirring freshly pre-fi cipitated and washed calciumsulphate ends.

5 to 10% solution of sodium .caseinogenate,

adding a small quantity of formaldehyde.

Example 3.To a solution of- 450 grams of gelatine in 2 litres of-wateris addeda solution of 750 grams of barium chloride in 1.5 litres ofwater, and, While stirring a solution of 420 grains of anhydrous sodiuming a solution of 80 grams of acid fuchsine in 2 litres of water.Instead thereof 125 grams of aurin in 1.5 litres of alcohol of 40 tostrength may be employed.

What I claim is,

1. A film for photographic work with visible 1i ht re s comprisin a su'orting flexible sgeet hgving on one side tligreof a coating of'materialsensitive to visible light rays and upon the other side a coating of acoating of material sensitive to visible light rays and upon the otherside a coating of gelatine containing finely grained particles-- in anamount and with a retouching.

grain size enabling 3. A film in accordance with claim and havingincorporated'in the colloid layer an antihalation dye.

4. A fihn in accordance with claim 2 and having incorporated in the'gelatine layer an antihalation dye.

In testimony whereof I affix my signature.

DR; WILHELM LoHoFER.

